For example, a high intensity discharge lamp (HID lamp) such as a xenon lamp and an extra-high pressure mercury lamp has been used so far, in a projector for image display such as a DLP™ projector and a liquid crystal projector, and a photo mask exposure apparatus. As an example, the principle of such a projector is shown in FIG. 16 (reference: Japanese Patent Application Publication No. 2004-252112 etc.).
As described above, light from a light source (UsA), which is made up of a high intensity discharge lamp etc., is inputted into an incident end (PmiA) of a light uniformizing unit (FmA) by, for example, using a condensing unit (not shown), which is made up of a concave reflection mirror, a lens, etc., and is outputted from an emission end (PmoA) thereof. Here, for example, an optical guide can be used as the light uniformizing unit (FmA), which is also called a rod integrator, a light tunnel, etc., and is formed of a prism made from light transmissive material such as glass, resin, etc., wherein while the light inputted into the incident end (PmiA) is repeatedly and totally reflected on side faces of the light uniformizing unit (FmA) according to the principle, which is the same as that of an optical fiber, it propagates inside the light uniformizing unit (FmA), thereby functioning so that the illuminance on the emission end (PmoA) is sufficiently uniformized even if distribution of the light inputted into the incident end (PmiA) has unevenness.
An illumination lens (Ej1A) is arranged so that a quadrangle image of the emission end (PmoA) is formed on a two-dimensional light amplitude modulation element (DmjA), whereby the two-dimensional light amplitude modulation element (DmjA) is illuminated by light outputted from the emission end (PmoA). However, in FIG. 16, a mirror (MjA) is arranged between the illumination lens (Ej1A) and the two-dimensional light amplitude modulation element (DmjA). And the two-dimensional light amplitude modulation element (DmjA) modulates light on a pixel to pixel basis according to an image signal so that the light is directed so as to enter the projection lens (Ej2A), or light is directed so as not to enter there, whereby an image is displayed on a screen (Tj).
Since the above-described two-dimensional light amplitude modulation element is also called a light valve, and in the case of the optical system shown in FIG. 16, a DMD™ (Digital Micromirror Device) is generally used as the two-dimensional light amplitude modulation element (DmjA).
The so-called fly eye integrator may be used as the light uniformizing unit, instead of the above-described optical guide. FIG. 17 shows the principle of a projector using this light uniformizing unit, as an example (reference: Japanese Patent Application Publication No. 2001-142141 etc.).
Light from a light source (UsB), which is made up of a high intensity discharge lamp etc., is inputted, as approximately parallel light flux, into an incident end (PmiB) of the light uniformizing unit (FmB) which is made up of a fly eye integrator, by using a collimator unit (not shown), which consists of a concave reflection mirror, a lens, etc. and is outputted from an emission end (PmoB). Here, the light uniformizing unit (FmB) is made up of a combination of an upstream fly eye lens (F1B) on an incident side, a downstream fly eye lens (F2B) on a light emission side, and an illumination lens (Ej1B). The upstream fly eye lens (F1B) and the downstream fly eye lens (F2B) are respectively formed by arranging, in vertical and horizontal directions, many quadrangle lenses whose focal distance is the same as one another and whose shape is the same as one another.
Each lens of the upstream fly eye lens (F1B), and each corresponding lens of the downstream fly eye lens (F2B), which is located downstream of each lens of the upstream fly eye lens (F1B), form an optical system called Koehler illumination, so that many Koehler illumination optical systems are aligned in a matrix in a plane. Generally, such a Koehler illumination optical system is made up of two lenses, wherein when the upstream fly eye lens collects light and illuminates an object face (a face to be illuminated), the upstream lens does not form an image of a light source on the object face, but forms an image of the light source on a center face of the downstream lens, whereby the object face is uniformly illuminated by arranging the downstream lens so as to form a quadrangle contour image of the upstream fly eye lens on the object face. The downstream lens functions so as to prevent a phenomenon in which an illuminance of a circumference part of the quadrangle object face falls depending on the size, if the downstream lens is not provided and a light source is not a perfect point light source but has a limited size, whereby it is possible to form a uniform illuminance on even the circumference part of the quadrangle object face by the downstream lens, independent of the size of the light source.
Here, since the optical system shown in FIG. 17 is configured based on case where approximately parallel light flux is inputted into the light uniformizing unit (FmB), an interval between the upstream fly eye lens (F1B) and the downstream fly eye lens (F2B) is set so as to become equal to those focal distances, so that an image of the object face of the uniform illumination of a Koehler illumination optical system is formed at infinity. However, since an illumination lens (Ej1B) is arranged downstream of the downstream fly eye lens (F2B), the object face can be pulled near on the focal plane of the illumination lens (Ej1B) from the infinity. Since the Koehler illumination optical systems arranged in a matrix in a plane are parallel to an incident light axis (ZiB) and light flux is approximately axisymmetrically inputted therein with respect to each central axis so that the output light flux is also approximately axisymmetrical, and outputs of all the Koehler illumination optical systems are imaged on the same object face on the focal plane of the illumination lens (Ej1B) because of the nature of lens, i.e., a Fourier transform of a lens, in which light rays entering a lens face at the same angle as one another, are refracted so as to be directed to the same point on a focal plane without depending on the incidence position on the lens face.
As a result, all the illuminance distributions in each lens face of the upstream fly eye lens (F1B) are overlaid, so that one synthesized quadrangle image, whose illuminance distribution is more uniform than that in case of one Koehler illumination optical system, is formed on the incident light axis (ZiB). The two-dimensional light amplitude modulation element (DmjB), which is an illumination object, is illuminated by light outputted from the emission end (PmoB) when a two-dimensional light amplitude modulation element (DmjB) is arranged at a position of the synthesized quadrangle image. However, a polarization beam splitter (MjB) is arranged between the illumination lens (Ej1B) and the two-dimensional light amplitude modulation element (DmjB) so that the light is reflected towards the two-dimensional light amplitude modulation element (DmjB) when the light is illuminated. And the two-dimensional light amplitude modulation element (DmjB) performs a modulation and reflection so as to or so as not to rotate the polarization direction of the light by 90 degrees on a pixel to pixel basis according to an image signal, whereby only the rotated light passes through the polarization beam splitter (MjB), and enters the projection lens (Ej3B), so that an image may be displayed on a screen (Tj).
In addition, in the case of the optical system shown in FIG. 17, in general, a LCOS™ (Liquid Crystal on Silicon) is used as the two-dimensional light amplitude modulation element (DmjA) in many cases. In the case of such a liquid crystal device, since only a component of light in a specified polarization direction can be modulated effectively, although a component parallel to the specified polarization direction is usually passed therethrough as it is, only a component perpendicular to the specified polarization direction is rotated by 90 degrees with respect to the polarization direction, so that the polarized-light alignment functional device (PcB) for making all the light effectively usable is inserted, for example, downstream of the downstream fly eye lens (F2B). Moreover, a field lens (Ej2B) is inserted immediately upstream of the two-dimensional light amplitude modulation element (DmjB) so that approximately parallel light may enter the two-dimensional light amplitude modulation element (DmjB).
In addition to the reflection type of the two-dimensional light amplitude modulation element shown in FIG. 17, a transmissive liquid crystal device (LCD) may be used as the two-dimensional light amplitude modulation element in the optical arrangement which is suitable therefor (reference: Japanese Patent Application Publication No. H10-133303 etc.).
Generally, for example, a dynamic color filter such as a color wheel is arranged upstream or downstream of the light uniformizing unit in a projector in order to display a color image, and the two-dimensional light amplitude modulation element is illuminated with color sequential light flux of R, G and B (Red, Green, Blue), whereby color display is realized in time dividing manner, or a dichroic mirror or a dichroic prism is arranged downstream of the light uniformizing unit, so that the two-dimensional light amplitude modulation element, which is independently provided in each color, is illuminated with light which is separated into the three primary colors of R, G and B, and a dichroic mirror or a dichroic prism for performing color synthesis of the modulated light flux of the primary colors R, G and B is arranged. However, for ease of explanation, in FIGS. 17 and 18, these elements are omitted.
However, the high intensity discharge lamp has drawbacks such as low conversion efficiency from applied power to light power, i.e., great calorific, and a short life span. A solid light source such as an LED and a semiconductor laser attracts attention in recent years as an alternative light source, in which these drawbacks are solved. Although of these light sources, in the LED, calorific loss thereof is smaller and an operating life span thereof is longer than those of the discharge lamps, since there is no directivity of light emitted therefrom as in the discharge lamps, there is a problem that the usage efficiency of light is low when it is used in the above-mentioned projector or exposure apparatus, in which only light in specific direction can be used. On the other hand, a semiconductor laser has high directivity in addition to a small calorific loss and a long operating life spam as in such an LED, so that there is an advantage that the usage efficiency of light is high, when it is used in the above-mentioned projector, exposure apparatus, etc. in which only light in a specific direction can be used.
When an optical device such as a projector is realized by using a solid light emitting element without regard to such a type of light sources, i.e. a semiconductor laser or a light emitting diode, since the light emission amount of one element thereof is small, it is necessary to mount two or more elements so as to realize predetermined light intensity by combining the light from each solid light emitting element. For the reasons, for example, Japanese Patent Application Publication No 2011-076781 discloses that two or more light sources are arranged so as to form rows and columns, the light source group is held at a light source holding member so that the optical axes of the light sources may be approximately parallel to one another, and the light source holding member is thermally connected to a heat sink through a heat transfer member. Moreover, for example, Japanese Patent Application No. 2005-129877 discloses a device in which two or more light emitting diodes are in series connected to one another.
When current is simultaneously applied to two or more solid light emitting elements, the series connection thereof becomes advantageous compared with the parallel connection thereof in view of cost reduction. There is a difference therebetween, as set forth below. That is, although, in case of the series connection, the voltage to be applied to all the connected solid light emitting elements becomes high since voltage for the number of connected solid light emitting elements is required, but current for only one solid light emitting element is enough to be passed therethrough, so that small current may be sufficient. On the other hand, although, in the case of the parallel connection, voltage for only one solid light emitting element is enough to be applied to all the connected solid light emitting elements, so that low voltage may be sufficient, but current to be passed therethrough becomes large since current for the number of the connected solid light emitting elements is required. It is known that in general, the efficiency of a circuit, in which a large current is passed, tends to be worse than that of a circuit, in which high voltage is generated, and the cost of the circuit, in which large current is passed, is higher than that of the circuit, in which high voltage is generated.
Unlike a white light source such as the high intensity discharge lamp, a solid light emitting element such as a light emitting diode and a semiconductor laser is a monochromatic light source, so that, for example, as disclosed in Japanese Patent Application Publication No. 2002-268140, it is necessary to prepare a solid light emitting element for each of R-G-B colors for colorization. Or instead of preparing such solid light emitting elements for two or more colors, for example, Japanese Patent Application Publication No. 2004-341105 discloses that a color wheel, in which phosphor layers are separately formed, and each layer emits fluorescence of R, G, or B color, is separately formed, is irradiated with ultraviolet light emitted from a solid light emitting element, which is a monochromatic light source, thereby forming color sequential light beam flux made up of each of R, G, and B colors. In addition, for example, Japanese Patent Application No. 2010-231063 discloses a color wheel, in which a phosphor layer for emitting fluorescence of each of R and G colors and a layer for transmitting or diffusing B color are formed in a divided manner, is irradiated with light emitted from a solid light emitting element which is a monochromatic light source and which emits blue light, thereby forming color sequential beam flux of each of R, G, and B colors. In addition, the solid light emitting element for emitting monochromatic light, and the color wheel which is the dynamic color conversion element, are used in order to simplify the structure thereof and to reduce the cost thereof, instead of using a solid light emitting element for two or more colors.
As mentioned above, although cost reduction of the light source device using a solid light emitting element has been attempted, it has not been sufficient. For example, in the above-mentioned case where the solid light emitting element which emits monochromatic light and a dynamic color transformation device are used, since the brightness of each of R, G, and B colors is not simply proportional to the brightness of incident monochromatic light, if light modulation is simply performed, the balance of each color will be lost, so that it is necessary to make a delicate balance adjustment of each color in order to compensate influence of deterioration of a phosphor. Or a delicate adjustment of balance of each color is required to perform an operation for quantitatively dropping the brightness of each of R, G, and B color according to the dimness in case of a dim video image, and to perform an operation for quantitatively dropping the brightness of G and B colors according to reddishness etc., in case of a reddish video image, when a capability of fine gradation reproduction is acquired under a condition where the number of reproduciable gradation levels of the above-mentioned two-dimensional light amplitude modulation element, is limited. However, when actually performing this operation, it is necessary to change the brightness of monochromatic light according to timing when colors are switched in dynamic color conversion. In this regard, the cost of the conventional light source apparatus is greatly depending on whether or not to insulate a host circuit which generates a modulation amount specifying signal which is a target control value of the brightness of monochromatic light, from an electric supply circuit which passes current through a solid light emitting element, and moreover depending on how the modulation amount specifying signal is transmitted in the case where they are insulated from each other. However, in a conventional light source equipment, the structure, which is optimal for such cost reduction, has not been configured. Also, refer to Japanese Patent Application Publication No. 2004-341105.